Bytownite
A plagioclase feldspar with 70-90% anorthite and 10-30% albite. Bytownite is at the "high" end of the series and has an RI slightly higher than that normally given for feldspar as a whole.
Physical properties:
| Chemistry: | Na[AlSi3O8] Ca[Al2Si2O6] |
| Hardness: | 6-6.5 |
| SG: | 2.74-2.75 |
| Cleavage: | Perfect, three directions |
| Fracture: | Somewhat brittle |
| Thermal sensitivity: | None |
Optical properties:
| RI: | 1.56-1.58 |
| Dispersion: | 0.012 (weak) |
| Double refraction: | 0.008 (weak) |
| Pleochroism: | None |
| Critical angle: | 40° |
Facet angles (pavilion/crown):
| Vargas: | 44°/42° |
| Olson: | 43°/42° |
| Soukup: | 43°/42° |
| Roth: | 43°/42° |
| MDR: | 43°/42° |
| Schlagel: | 43°/39° |
| Hashnu: | 43°/42° |
| Sinkankas: | 43°/40-50° |
| GIA: | 43°/42° |
| Perkins: | 43°/39° |
| Raytech: | 43°/42° |
Cutting lap:
Medium or fine
Faceting polishing:
| Vargas: | Cerium oxide on acrylic, Aluminum oxide on tin/lead |
| Olson: | Tin oxide on acrylic |
| Christiansen: | Aluminum oxide on tin/lead, Cerium oxide on acrylic, Tin oxide on tin |
| Perkins: | Aluminum oxide on BATT or Corian |
| Raytech: | Cerium oxide on Fast Lap, phenolic or acrylic |
Cabochon polishing:
| Olson: | Tin oxide on felt |
| Christiansen: | Aluminum/cerium oxide on leather or felt |
| Cox: | Cerium oxide on felt |
| Covington: | Cerium oxide on felt |
Orientation:
After shape. Usually, even the table facet does not need to be oriented away from the cleavage plane.
Treatments/synthetic:
None known (some sources claim that Chinese andesine is heat-treated bytownite from Mexico)
Tips!
Sometimes it can be difficult to polish - try using a LightningLap CeOx for better results.
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